1. Field of the Invention
The present invention relates to a post-processing device and an image forming apparatus including the same.
2. Related Art
Among conventional image forming apparatuses, there are those that include a post-processing device which performs post-processing on a sheet of medium on which an image has been formed in an image forming apparatus, such as a copy machine and multi-functional machine. Such a post-processing device includes a pair of feed rollers that feeds a sheet of medium in a feed direction so as to be stacked on a tray, and a sheet aligning mechanism that causes the sheet of medium fed from the pair of feed rollers to move in a shift direction (direction orthogonal to the feed direction and a sheet stacking direction), so that the sheet of medium is aligned at a predetermined position on the tray.
For example, a sheet aligning mechanism has been known that causes a pair of alignment members to rotationally and rectilinearly move to be on standby at an alignment waiting position, before causing the sheet of medium fed from the pair of feed rollers to be located between the pair of alignment members. Then, the sheet aligning mechanism causes one alignment member to push the fed sheet of medium in parallel to the shift direction from one alignment waiting position, thereby the one alignment member causing the sheet of medium thus pushed to abut the other alignment member at the alignment waiting position. In this manner, the sheet aligning mechanism performs positioning of the sheet of medium in the shift direction.
Such a sheet aligning mechanism includes the pair of alignment members configured to be rotationally and rectilinearly movable, relative to an alignment axis that has a length greater than a width of the sheet of medium (dimension in the shift direction).
A stepping motor is used in a shift drive portion that causes the pair of alignment members to move in the shift direction, and in a rotational drive portion that causes the pair of alignment members to rotate around a rotation shaft. The stepping motor has extremely high tracking performance to input signals, and thus is controlled by an open loop. Therefore, in order to curb manufacturing costs of image forming apparatuses, detectors to detect positions of the pair of alignment members, which are control objects of the shift drive controller and the rotational drive controller, are rarely built into such image forming apparatuses.
Since the detection of positional information of the pair of alignment members is not carried out, it is likely that the positions of the pair of alignment members may shift from objective positions to be controlled when the sheet of medium stacked on the tray comes in contact with the pair of alignment members under control.